1. Technical Field
The present invention relates to a liquid droplet discharge apparatus, a mask pattern, and a liquid droplet discharge method.
2. Related Art
As an example of an existing liquid droplet discharge apparatus, an ink jet printer that records (prints) an image by discharging ink droplets onto media of various types such as paper, and a film or the like and forming a plurality of dots on the media has been known. For example, the ink jet printer alternately repeats main scanning and sub scanning. In the main scanning, a head on which a plurality of nozzles are formed is caused to discharge ink droplets through the nozzles while being moved in a main-scanning direction relatively to the medium so as to form dot rows (raster lines) aligned in the main-scanning direction of the medium. In the sub scanning, the medium is moved (transported) in a sub-scanning direction intersecting with the main-scanning direction. With the main scanning and the sub scanning, dots are aligned on the medium in the main-scanning direction and the sub-scanning direction densely, so that an image is formed on the medium.
For example, JP-A-11-245384 discloses a recording apparatus in which an image region that is formed by main scanning of a head and an image region that is formed by subsequent main scanning overlap with each other on a boundary portion and a state where 100% printing is performed shifts to a state where no printing is performed toward nozzles on end portions of the head on the overlapped boundary portion. The recording apparatus can avoid drastic deterioration in image quality even when the boundary portion varies with a transportation error of sub scanning.
However, the liquid droplet discharge apparatus (recording apparatus) as disclosed in JP-A-11-245384 forms an image by triple main-scanning and discharges liquid droplets (ink droplets) through the nozzles in a state where the liquid droplets are discharged on image regions with 100%-printing other than the boundary portions. When the main scanning is performed in a state where the liquid droplets of 100% are discharged, the liquid droplets that are simultaneously discharged through all the nozzles along the sub-scanning direction become obstacles and turbulence is generated at the rear side of the liquid droplets. The turbulence causes band-like density unevenness (hereinafter, image defect with the density unevenness is referred to as “wind ripple”), that is, density is relatively higher than peripherals on the medium due to satellites having small masses in some cases. This arises a problem that the image quality is lowered.